LYTIC AND LYSOGENIC CYCLE NEW.pptxyuhyuh

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1. LYTIC AND LYSOGENIC CYCLE DHANUSHIKA.L 24PBO105

2. Bacteriophage

3. Lytic life cycle

4. Attachment Infection takes place by random collision between the phages and the bacterium. The tail fibers select specific site on the surface of the bacterium. The spikers anchor firmly. A hole is made in the cell wall of bacterium by the enzyme lysozyme secreted by the tail.

5. Penetration The sheath contracts and this causes the tail core to penetrate the cell wall. The DNA of the head is discharged into the cell through the tail core. The protein coat does not enter in it remains outside the cell.

6. Synthesis The DNA of the phage takes over the protein synthesizing machinery of the bacterium. The host DNA is degrated by the viral deoxyribonuclease .

7. Assembly and maturation Viral DNA also replicates to produce hundreds of copies. Each DNA copy is enclosed by a protein coat producing new virus.

8. Release Soon the bacterial wall ruptures and the new viral particles are released. A single phage can produce about 200 phages in twenty minutes after infection

9. Lysogenic life cycle

10. All the lambda series bacteriophage exhibit lysogenic cycle. In lysogenic cycle the bacterium is not lysed . As in the lytic cycle the viral DNA enters the bacterium cell. But the viral DNA does not take over the protein synthesizing machinery of the host.

11. Instead it gets integrated with the bacterial chromosome. at this stage, the virus is called prophage . The bacterium with prophage is called lysogenic and it is resistant to other phages . The viral DNA replicates along with the bacterial chromosome. Rarely, the prophage DNA can disintegrate and enters into lytic cycle.